This invention relates to an improvement of a color picture tube, wherein a set of three electron beams for emitting red, green and blue lights, respectively, is emitted from a three-beam type electron gun, and passing through a vertically oblong slot of a shadow mask, is led to a black matrix-type screen standing behind the shadow mask so as to energize selectively any of three color-luminous strips which form a set of each three colors on said screen to correspond to said set of three electron color-beams and to produce desired color-lights.
Apertures of the shadow mask of the color picture tube of this type characterizing the vertically slotted mask as described above are formed in vertically oblong slots. Consequently, as compared with the ordinary-type color picture tubes employing masks having ordinary round apertures, it is already known that this type of tube can select larger ratio of apertures for the mask. Accordingly not only does it reduce electricity wastefully consumed by a portion of the electrons striking the mask and failing to pass through it, but also it is able to produce brighter pictures on the screen. Besides, it has the advantage of being almost free from color derangement in the vertical direction even in case of thermal expansion of the shadow mask.
However, in the known construction of this type of color picture tube, its screen has the form of massed vertical stripes of red, green and blue luminous strips alternately arranged to emit lights of the respective colors when energized. And furthermore, the light-absorbing film placed in the gaps between the luminous strips for the purpose of improving the contrast serves only to form vertical stripes on the screen. Therefore, it entails the shortcoming of deteriorating pictures coming out on the screen by distinct vertical stripes. Besides, the area covered by the light-absorbing film on the screen is not sufficient, and accordingly the improving effect on the contrast is not satisfactory either.